Glass laser materials

ABSTRACT

A SILICATE GLASS FOR USE AS A GLASS LASER MATERIAL DOPED WITH TRIVALENT NEODYMIUM CONTAINS SB2O3 AS WELL AS TIO2, MOO3, NB2O5, WO3, BI2O3 AND/OR TA2O5. THE COMBINATION OF THESE COMPONENTS PREVENTS DETERIORATION IN LASER PERFORMANCE DUE TO SOLARIZATION.

M) 1972 MASAHIKO ISHIYAMA 3,677,960

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m saJ /(p Z 57 B QM aud States Patent O 1 3,677,960 Patented July 18, 1972 ABSTRACT OF THE DISCLOSURE A silicate glass for use as a glass laser material doped BACKGROUND OF THE INVENTION This invention relates to a neodymium doped glass laser material, more particularly, the invention relates to a silicate glass forjuse as a glass laser material doped with trivalent neodymium, and particularly to the prevention of deteriorations in laser performance of the glass due to solarization.

DESCRIPTION OF THE PRIOR ART A neodymium-doped glass laser is known tov be an excellent solid laser, for it functions at room temperature with a low threshold energy and is even capable of continual emission.

Furthermore, this glasslaser is less expensive than lasers composed of crystals such as of ruby, and glass offers the advantage that" it can be easily fabricated into large rods...

Recently, the "neodymium-doped glass alser has been used as a" giant pulse laser and, as such, is being required to produce an ever higher output energy. To yield a high output energy, there is required a high input energy, that is to say, exposure to an intense flash of light such as one originating from axenon flash-lamp. Such an intense light contains a" large amount of ultraviolet radiation. 7 I e A glass'laser rodwhich has been repeatedly exposed to ultraviolet radiation undergoes aprocess known as solarization and is more or less browned. This peripheral discoloration of the rod is necessarily accompanied by an increase in input threshold energy and a decrease in output'energy of thelaserL In,the production 'of glass, antimony oxide (Sb O has beenconventionallyadded for the removal of bubbles and, in glass laser's, this compound has been believed to prevent solarization in some measure. However, my study has shown thattheanti-solarization effect of Sb O hood of 5800 angstrom units, and this dominant absorption is masked by the increase in absorption by the glass itself in the visible region of the spectrum, with the result that the efiiciency of the laser is reduced. In addition, because about 40 percent of the energy used for the excitation of Nd is derived from light of wavelengths shorter than 4000 angstrom units, it is necessary, also, to prevent the solarization in the ultraviolet region.

SUMMARY OF THE INVENTION neodymium-doped glass laser material which will not suffer a reduction in laser performance due to solarization even on repeated laser emission.

Another object of this invention is to provide a neodymium-doped glass laser material comprising silicate glass with constituents conducive to the prevention of solarization in the ultraviolet to visible region of the spectrum.

Other objects and advantages of this invention will become apparent as the following description of the invention proceeds.

Thus, this invention provides a neodymium-doped glass laser material based on silicate glass which is substantially free of solarization after repeated exposure to intense light, said silicate glass containing, in a combined total proportion not exceeding 20 percent by weight of the glass, from 0.5 to 10 percent by weight of antimony oxide (Sb O and at least one oxide selected from the group consisting of from 4 to 15 percent by weight of titanium oxide (TiO from 0.2 to 15 percent by weight of molybdenum oxide (M00 from 0.2 to 15 percent by weight of nibium oxide (Nb O from 0.2 to 15 percent by weight of tungsten oxide (W0 from 0.2 to 15 percent by weight of bismuth oxide (Bi O and from 0.2 to 15 percent by weight of tantalum oxide (-Ta O BRIEF DESCRIPTION OF THE DRAWINGS FIGS. l'through 12 show the spectral transmission curves of the twelve glass plate samples given in Table 1 of Example 1, respectively, before and after irradiation with light from a xenon fiashlamp.

FIGS. 13 through 16 show the output energy curves plotted against input energies before and after the emission of glass lasers made from four of the glass samples.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Silicate glass is used as the base glass for the neodymium-doped glass laser material. More particularly, use is made of soda-lime glass (Na O--'CaOSiO barium crown glass (K OBaO-SiO or, if a monovalent metal oxide, divalent metal oxide and trivalent is substantially limited to the visible region of the specso rption'by the activating agent Nd is in the neighbormetal oxide are designated as R 0, R0 and R 0 respectively, the silicate glass formula may generally be written as R ORO-SiO or R ORO-R O -SiO. In the base glass composition, R 0 may be Li O, Na O or/and K 0, RO may be CaO, MgO, BaO or/ and SrO, and R 0 may be A1 0 or/ and B 0 The amount of the neodymium to be doped as an activating agent onto base glass is preferably in the range of frorn 0.25 to 8 percent by weight in terms of Nd O the optimum proportion being from 2 to 6 percent by weight on the same basis.

The preferred and optimum ranges of these components in the glass laser material of this invention are as follows on a percent by weight basis.

Regarding the Si content of the glass, it it exceeds 75 percent by weight, the viscosity of the glass will be too high for efiicient melting, while the presence ofSiO in an amount less than 50 percent by weight will cause reductions in chemical durability and fluorescent intensity of the glass, and a reduction in laser performance due to the reduced fluorescent lifetime.

If the amount of R 0 is in excess of 40 percent by weight, the glass will suffer a reduction in chemical durability and is liable to get devitrified. If the R 0 content of the glass is less than 5 percent by weight, the viscosity of the glass melt will be increased and the fluorescent lifetime of the glass will be reduced.

The presence of RO is conductive to improvements in both chemical durability and melting characteristics of glass, but the glass is ready to devitrify as the amount of R0 exceeds 25 percent by weight. The fluorescent intensity and fluorescent lifetime of glass will also be reduced under such conditions.

Though A1 0 or B 0 is an optional additive, the presence of either of them in a proportion of more than 10 percent by weight will shorten the fluorescent lifetime of glass. 0

In accordance to this invention, to prevent solarization of the glass laser material having the described composition, Sb O and at least one oxide selected from the group consisting of TiO M00 Nb O W0 Bi O and Ta O are incorporated in the material in a combined total proportion of not exceeding 20 percent by weight relative to the total glass. My studies have shown that the latter group of oxides are capable of absorbing ultraviolet rays of comparatively long wavelengths; while Sb O is not. This fact is ascertained by measurements of spectral transmissions of glass samples containing those oxides. For example, in the of a 3 millimeter-thick glass plate containing 1 percent by weight of Sb O the absorption edge wavelength, that is the wavelength below which light will not be transmitted is 290 m In contrast, the absorption edge wavelengths spectral transmission curve for glass samples containing 5 percent by weight of TiO or 5 percent by weight of M00 are 319 mg and 336 m respectively.

When excited by exposure to light from a xenon flashlamp, glass lasers containing any of the oxides of Ti, Mo, Nb, W, Bi and Ta absorb light of comparatively high input energy inevitably lead to reductions in output energy.

On the other hand, the conventional glass laser containing the oxide of Sb alone is vulnerable to solarization under exposure to radiation of wavelengths longer than the aforementioned absorption edge and, therefore, if the glass laser is excited by a xenon flashlamp, the laser is easily degraded.

However, it has been discovered that if the oxide of Sb is present in glass along with the oxide of any one of Ti, Mo, Nb, W, Bi and Ta as specified according to this invention, the resulting glass laser will be completely or substantially free of solarization under an extremely high input energy.

It appears that the presence of the two oxides yields a synergistic effect.

The oxides to be incorporated in glass for the purpose of preventing the solarization of glass lasers will hereinafter be generally called anti-solarizers or anti-solarizing agents.

The permissible ranges and preferred ranges of antisolarizers, when used singly and independently, are shown below on a weight percent basis.

The lower limit for each anti-solarizer is prescribed because the particular anti-solarizer will not be effective in the prevention of solarization when it is used in amounts less than that limit, while the upper limit is prescribed for the reason that, if it occurs in any amount in excess of the limit, it will be diflicult to manufacture a homogeneous glass and the fluorescent intensity of the product will be too low to ensure a satisfactory laser performance. It is for the same reasons as stated above that the combined amount of anti-solarizers is restricted to no more than 20 percent by weight and, preferably, to no more than 10 percent by weight. 7

It should be understood, in this connection, that the following components are undesirable in base glass for the production of the glass laser of this invention.

Thus, As O Pr O PbO, Ag O, Yb O S and I should not be present in a combined amount in excess of aboutl percent by weight, for they tend to promote solarization of glass. The concentration of components giving absorptions at the emission wavelength (1.06 of the neodymiumdoped glass laser, such as CuO, FeO, Sm O V 0 U0 etc. should not exxceed approximately 0.1 percent by weight. Furthermore, the concentration of components giving intense absorptions in the visible region ,Of the spectrum, such as Cr O C0 0 M 0 and MnO should not exceed the limit of about 0.1 percent, for they tend to mask the Nd which is the activating agent of the glass laser, and interfere with its excitation.

The following examples are given to further illustrate I this invention and should by no means be construed as being limitative of the scope of the invention'which is particularly set forth in this specificationand the claims appended thereto.

i assanigsie Nam; 3,4 ands containing T1o ,Moo -,wo j and ;TiO -l Nb O respectively, as will be seen from .11 the sarnples, butthe molar ran er, M 0, CaQand duewsolaezauoe P XP W- sioz were Jhlfl in sample 1 oandol in Sambles 5 In contrast, the glass samples according to this invena g v tron, herein designated as Sample No. '6 to N0. 12, which Thosejglasssampleswere prepared as followsfA batch contam'sbzoil and of T102 M003 M3203.

' r -I. Bi 'Ta'O or a Iriixture'thereof as Will be seen from of rea ent ade raw materials was heated ma latmum 3 1 crucibl e at l lSO" C. for 4"hours whereby illian-was I S. through. .shqw 2 reductlonsnor. y prepared The melt was homogenized bystirringwith a f t e F .9 m transmlsslon, on exposumklt platinum stirrer and cast into a-platefThis glass plate P g l t n f fl f ti hee 'e' m??? was annealeda'nd polished to a finished size oft-2 x 10x 3 9$.-! W as mk a emas a the l 2 millimeters t taming sb O and M00 (Sample Nos; '6, 7 and8) show The glas's Plates while being cooled with water were practically no reductions in transmission due to solarizaa a ,1, repeatedly exposed to light from a helical xenon fiashlamp. The energy for the xenon flashlamp wastab'tained' ,EXAMEDLE 2 from a power supply containing capacitors. in this test, From the glass samplesdesignated as Sample Nos. 1, the capacitance of the power supply wasconstantat 100 3.2, T6. and 8, (Table 1), glass rods 10( millimeters long f. and the voltage was also constant at i kv. 4m energy, and 6.5 millimeters in diameter were prepared and both of 1250 joules was supplied to'the 1ampfnach saihple" ends" of each rod were polished to a close tolerance. Each was irradiated 100 or 1600 times at intervals of from 12 rod was provided with reflectors of 100% and reto 15 seconds. .7 I 5; fiectivities, spaced apart from both ends, and was placed TA E-1.

Glass composition (percent by weight) SampleNumber 1 I "2 3 4 W15 2 7 6 9 10 11 12 Component: e

Base glass component SiOz NanO OaO Activating agent: N Anti-solarizer:

The number exposu between two straight cylindrical xenon flashlamps. is set forth below. i- 'Co0li1nhg vi ater was passed between thle1 rod and flash- V .1 amp.-; e. aser re s were excited wit input energies Samp 16 Numbers of repeated-g from, about 500 joules to 1500 joules at intervals of 12 i 1600 tol5 s'e coiids, and 50 to 300 repeated emissions were 3 1600 induced.

4 1600 50 The output energies before and after this repeated 5 100 laser emission were measured to ascertain the possible 6 I 100 deterioration in laser performance due to solarization.

7 1,600 FIGS. 13, 14, 15 and 16 show the output energy curves 8 1,600 of glass lasers made from Sample Nos. 1, 2, 6 and 8, 9 1,600 respectively, in which the input energy (energy fed to the .10 1600 on flashlamp) was plotted on the horizontal axis and 11 1,600 the output energy on the vertical axis. In each instance, 12 1600 the output energy after 50 repeated emissions is represented by black triangles, the output energy after 100 The spectral transmissions of each sample b f and emissions by white circles; and the output energy after after exposure Were measured with a Spectrophotometer 300 emissions by white triangles. It should be understood at an Optieal P of 3 millimeters to exa e degree that since there was no reduction in output energy in of solarization that had taken place as a result of exthe case of s l 6 d Na 8 (FIGS, 15 and 1 posure. only the output energies before emission and after 300 FIGS. 1 through 12 show the spectral transmission 5 emissions were plotted curves of the corresponding sample glass Plates at Wave The glass laser made from Sample 1 glass containing lengths from 340 to 700 mg. The numbers of the rfigures only 1 percent by Weight of sbzoa suffered a Significant correSp-ond to the Samp-le numbers The Curves shown by reduction in output energy due to the repeated emission. the sohd and dotted lines represent the spectral trans- For example with an input gy of 1500 joules t missions of each sample before and after exposure, ret t Der a ed b about 50 nt as meashred specti-vely. Where the solid line coincides with the dotted Pu e g PP Y P line, that is if there is no diifeience 1in transiirliission before zg g igg s lss zr gf gaggle No 2 which contains e, th solid ine a one is s own.

l lazi i lsam le No. 1 containing Sb 'O as an 5% by weight of 2 alone. when the p energy was exclusive anti-solarizer, and the glass samples designated about 1200 joules, the output energy dropped by about 30 percent as measured after 300 emissions. (See FIG. 14.)

This is in sharp contrast to the glass lasers of this invention which showed no reduction in output energy even after 50-300 emissions (see FIGS. 15 and 16).

EXAMPLE 3 amount of said antisolarizing agents being not greater than 10%.

3. A glass as set forth in claim 1, wherein the remainder of said glass other than said antisolarizing agents essentially consists of 50%75% SiO 5%40% Li O+Na O+K O, %-25%. CaO+MgO+BaO+SrO, 0%-10% A1 0 0%-l0% B 0 and 0.25%-8% Nd O 4. A glass as set forth in claim 1, wherein said at least one oxide is M00 Nb O W0 or Ta O 5. A glass as set forth in claim 1, wherein said at least one oxide is Bi o 6. A glass as set forth in claim 1, wherein said at least one oxide is TiO Glass composition (percent by weight) I claim:

1. A silicate glass doped with trivalent neodymium suflicient for use of the glass as a laser material and containing, as antisolarizing agents, not more than 20% of a combination of 0.5%10% Sb O with at least one oxide selected from the group consisting of 4%-15% TiO 0.2%15% M00 0.2%-15% Nb O 0.2%-15% W0 0.2%15% Bi O and 0.2%-15% Ta O all percentage figures being by weight of said glass.

2. A glass as set forth in claim 1, wherein said combination essentially consists of 0.5%-2.0% Sb O and at least one oxide selected from the group consisting of 4%10% TiO and 0.5%-10% M00 the combined References Cited UNITED STATES PATENTS TOBIAS E. LEVOW, Primary Examiner M. L. BELL, Assistant Examiner US. Cl. X.R. 10652 

